UVA442-Matrix Chain Multiplication

题目链接：https://vjudge.net/problem/UVA-442

紫书代码：

#include<cstdio>
#include<string>
#include<algorithm>
#include<iostream>
#include<stack>
using namespace std;

struct Matrix
{
    int a,b;
    Matrix(int a=0,int b=0):a(a),b(b) {}
}m[26];

stack<Matrix> s;

int main()
{
    int n;
    cin>>n;
    for(int i=0;i<n;i++)
    {
        string name;
        cin>>name;
        int k=name[0]-'A';
        cin>>m[k].a>>m[k].b;
    }
    string expr;
    while(cin>>expr)
    {
        int len=expr.length();
        bool error=false;
        int ans=0;
        for(int i=0;i<len;i++)
        {
            if(isalpha(expr[i]))s.push(m[expr[i]-'A']);
            else if(expr[i]==')')
            {
                Matrix m2=s.top();s.pop();
                Matrix m1=s.top();s.pop();
                if(m1.b!=m2.a){error=true;break;}
                ans+=m1.a*m1.b*m2.b;
                s.push(Matrix(m1.a,m2.b));
            }
        }
        if(error)printf("error
");
        else printf("%d
",ans);
    }
    return 0;
}